Well, it used to be that way. If you kept things current, you didn't need to install the SP, just keep on doing the minor updates. But they found that there were some instances that some machines weren't current. They found that including the SP's in the normal push they could catch those systems. To justify it, they include some extra updates to make the system current.
Also, if you ever rebuild your system, or get a new system don't turn on auto updates in the beginning (sound counter intuitive doesn't it?). Just manually download the SP's first (for the O/S and Office), and install them. THEN turn on auto updates. Saves time and multiple reboots.